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Physiology the ‘Root Cause’ Of Potatoes’ Unique Nutrient Needs

Managing nutrients for optimal potato crop health, yield and quality is challenging. The demands of tuber formation and the limitations of short, inefficient roots mean potatoes have nutrient requirements very different than most other major North American crops. Understanding how a potato plant processes nutrients in every growth stage; taking into account the potato type, variety and one’s specific environmental conditions; and forming a comprehensive nutrient management plan are all key factors in ensuring a crop is fertilized for success.

While potato genetics are diverse and root architecture varies greatly by type, variety and growing environment, potatoes generally have shallow roots that are relatively inefficient at foraging nutrients. Typically, a potato plant’s root length is only about 70 per cent as long as a sugar beet plant’s roots, and only 40 per cent the length of a wheat plant’s roots. Additionally, a potato plant’s root hairs, which are key to nutrient uptake, make up only 21 per cent of its total root mass, compared to 30 per cent in sugar beets and 60 per cent in winter wheat.

Mobile nutrients like nitrogen and sulfur can usually find their way to potato roots so do not need to be banded for improved efficiency. Unfortunately, ensuring adequate nitrogen and phosphorus all season is not always as easy as applying and ignoring. Leaching of nitrogen and the potential tie up of phosphorus can occur in many soils. And, applying full season amounts of nitrogen early in the season often leads to excessive vegetative growth, delayed tuber initiation and delayed maturity.

To avoid excessive crop growth and to limit potential losses, growers should consider applying a portion of the nitrogen at planting and the majority after crop emergence. Other mobile nutrients like sulfur can be managed similarly.

Non-mobile nutrients typically offer best nutrition to potato crops when they are band-applied near or at planting.  The bands need to be placed in a soil location where maximum feeder-root activity occurs but not so close to seed pieces to cause injury.  If these nutrients cannot be banded, it is recommended they be thoroughly incorporated through the active rooting zone.

Potato plants demand significant phosphorus. The actual amount required can vary widely based on variety, soil pH, and environmental conditions. During bulking, phosphorus uptake can range from 0.28 to 0.82 pounds per day per acre. Since bulking typically lasts 70 to 100 days, total uptake in this growth stage can be as low as 19.6 lbs/ac or as high as 82 lbs/ac.

Phosphorus is a non-mobile nutrient that is best band-applied in the root zone immediately prior to planting.  High levels of soluble phosphorus near a fertilizer band does not stimulate excessive vegetative growth but can tie up nutrients like zinc or become tied up in soil as insoluble mineral. To compensate, most growers apply a higher rate, apply multiple applications or opt for slow-release formulations.

Slow-release fertilizers offer a continuous nutrient flow throughout all potato growth stages, ensuring adequate nutrient availability all season long. Slow-release fertilizers also prevent rapid dissolution of nutrients early in the growing season, which can lead to nutrient imbalance and/or potential losses via soil fixation or movement outside of the root zone.

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